Influence of inter-observer delineation variability on radiomics stability in different tumor sites.

BACKGROUND: Radiomics is a promising methodology for quantitative analysis and description of radiological images using advanced mathematics and statistics. Tumor delineation, which is still often done manually, is an essential step in radiomics, however, inter-observer variability is a well-known uncertainty in radiation oncology. This study investigated the impact of inter-observer variability (IOV) in manual tumor delineation on the reliability of radiomic features (RF). METHODS: Three different tumor types (head and neck squamous cell carcinoma (HNSCC), malignant pleural mesothelioma (MPM) and non-small cell lung cancer (NSCLC)) were included. For each site, eleven individual tumors were contoured on CT scans by three experienced radiation oncologists. Dice coefficients (DC) were calculated for quantification of delineation variability. RF were calculated with an in-house developed software implementation, which comprises 1404 features: shape (n = 18), histogram (n = 17), texture (n = 137) and wavelet (n = 1232). The IOV of RF was studied using the intraclass correlation coefficient (ICC). An ICC >0.8 indicates a good reproducibility. For the stable RF, an average linkage hierarchical clustering was performed to identify classes of uncorrelated features. RESULTS: Median DC was high for NSCLC (0.86, range 0.57-0.90) and HNSCC (0.72, 0.21-0.89), whereas it was low for MPM (0.26, 0-0.9) indicating substantial IOV. Stability rate of RF correlated with DC and depended on tumor site, showing a high stability in NSCLC (90% of total parameters), acceptable stability in HNSCC (59% of total parameters) and low stability in MPM (36% of total parameters). Shape features showed the weakest stability across all tumor types. Hierarchical clustering revealed 14 groups of correlated and stable features for NSCLC and 6 groups for both HNSCC and MPM. CONCLUSION: Inter-observer delineation variability has a relevant influence on radiomics analysis and is strongly influenced by tumor type. This leads to a reduced number of suitable imaging features.

Potential dosimetric benefits of adaptive tumor tracking over the internal target volume concept for stereotactic body radiation therapy of pancreatic cancer.

BACKGROUND: Radiotherapy for pancreatic cancer has two major challenges: (I) the tumor is adjacent to several critical organs and, (II) the mobility of both, the tumor and its surrounding organs at risk (OARs). A treatment planning study simulating stereotactic body radiation therapy (SBRT) for pancreatic tumors with both the internal target volume (ITV) concept and the tumor tracking approach was performed. The two respiratory motion-management techniques were compared in terms of doses to the target volume and organs at risk. METHODS AND MATERIALS: Two volumetric-modulated arc therapy (VMAT) treatment plans (5 × 5 Gy) were created for each of the 12 previously treated pancreatic cancer patients, one using the ITV concept and one the tumor tracking approach. To better evaluate the overall dose delivered to the moving tumor volume, 4D dose calculations were performed on four-dimensional computed tomography (4DCT) scans. The resulting planning target volume (PTV) size for each technique was analyzed. Target and OAR dose parameters were reported and analyzed for both 3D and 4D dose calculation. RESULTS: Tumor motion ranged from 1.3 to 11.2 mm. Tracking led to a reduction of PTV size (max. 39.2%) accompanied with significant better tumor coverage (p<0.05, paired Wilcoxon signed rank test) both in 3D and 4D dose calculations and improved organ at risk sparing. Especially for duodenum, stomach and liver, the mean dose was significantly reduced (p<0.05) with tracking for 3D and 4D dose calculations. CONCLUSIONS: By using an adaptive tumor tracking approach for respiratory-induced pancreatic motion management, a significant reduction in PTV size can be achieved, which subsequently facilitates treatment planning, and improves organ dose sparing. The dosimetric benefit of tumor tracking is organ and patient-specific.

Tumor stage, tumor site and HPV dependent correlation of perfusion CT parameters and [18F]-FDG uptake in head and neck squamous cell carcinoma.

BACKGROUND AND PURPOSE: This study investigated whether tumor perfusion, FDG uptake and their correlation depend on tumor stage, site and HPV in head and neck cancer. MATERIAL AND METHODS: 41/55 eligible patients with integrated FDG-PET/perfusion CT from 2 prospective studies were assessed. A GTV(CT) and GTV(PET) were created. Perfusion maps were calculated using singular value decomposition method. Blood volume (BV), blood flow (BF), mean transit time (MTT) and standardized uptake value (SUV) in the tumor were compared to the surrounding tissue using Wilcoxon test and Spearman correlation of perfusion and SUVmean in the tumor was studied (p=0.05). RESULTS: Perfusion parameters were significantly increased in the GTV(CT) of advanced tumors in comparison to the surrounding soft tissue (p<0.01). Oral cavity and oropharyngeal cancer showed a higher BF than laryngeal cancer (p<0.04). No correlation between perfusion and SUVmean was found, however SUVmean correlated significantly with BF for the HPV-positive tumors (r=0.86, p=0.04) and with BV for the oropharyngeal cancer (r=0.63, p=0.05). CONCLUSION: Tumor stage, site and HPV are associated with different perfusion or combined perfusion/SUV signatures. Further studies are needed to investigate if these signatures co-determine clinical outcome.

Long-term safety and efficacy of fractionated stereotactic body radiation therapy for spinal metastases.

PURPOSE: Patients with long life expectancy despite metastatic status might benefit from long-term local control of spinal metastases. Dose-intensified radiotherapy (RT) is believed to control tumor growth better and thus offers longer pain relief. This single-institution study reports on fractionated stereotactic body radiation therapy (SBRT) for spinal metastases in patients with good life expectancy based on performance status, extent of metastases, histology, and time to metastasis. METHODS: Between 2004 and 2010, 36 treatment sites in 32 patients (median age 55 years; male 61%; median Karnofsky performance score 85) were treated with fractionated SBRT. The median treatment dose was 60 Gy (range, 48.5-65 Gy) given in a median of 20 fractions (range, 17-33); the median maximum dose to the planning risk volume for the spinal cord (PRV-SC) was 46.6 Gy. RESULTS: All patients suffering from pain prior to RT reported pain relief after treatment; after a median follow-up of 20.3 months, 61% of treatment sites were pain-free, another 25% associated with mild pain. In 86% of treatments, patients were free from neurological symptoms at the time of the last clinical follow-up. Acute grade 1 toxicities (CTCAE 3.0) were observed in 11 patients. Myelopathy did not occur in any patient. Radiologically controlled freedom from local progression was 92 and 84% after 12 and 24 months, respectively. Median overall survival (OS) was 19.6 months. CONCLUSION: Patient selection resulted in long OS despite metastatic disease, and dose-intensified fractionated SBRT for spinal metastases was safe and achieved long-term local tumor control and palliation of pain.